1. Field
The present application relates to a noise reduction filter processing circuit, an image processing circuit, an imaging device, and a noise reduction program for reducing a color noise generated in an acquired image.
2. Description of the Related Art
Digital cameras mounting an image sensor consisting of a photoelectric conversion element, such as a CCD (Charge Coupled Device) or a CMOS (Complementary Metal-Oxide Semiconductor), are generally provided. In recent years, as the size of an image sensor is reduced or the pixel density of an image sensor is increased, the pixel pitch has been minimized, and a noise, such as a dark current noise or a photon shot noise of the image sensor, is generated significantly. The noise includes a point-like luminance noise generated in a luminance signal or a patchy color noise generated in a color signal. Among these noises, the color noise is a low frequency random noise which is a factor for causing degradation in the image quality. Therefore, a method for reducing the color noise in an image using a low pass filter is typically used (for example, refer to Japanese Unexamined Patent Application Publication No. 2003-123063).
However, when the color noise is reduced using a low pass filter, not only a deviation in a hue direction but also a deviation in a saturation direction is reduced. Specifically, when an image has color information wherein color information of each pixel is complementary with each other, in an image subjected to color noise reduction processing by a low pass filter, the color information of each pixel becomes similar to achromatic information, resulting in an image color different from the original image color.